Plural component dispensing apparatus

ABSTRACT

A dispensing apparatus ( 10 ) is capable of robotically dispensing plural component materials such as sealants and adhesives with the same precision as single component products and yet will maintain ratio assurance and integrity for mixing the two materials. First look at the flow rate and if the flow rate is too high, decrease is needed on one of the components. The ratio error is then looked at and the flow rate/pressure differential for the material which is there in excess is decremented. Another level of control is provided in that the ratio error is continually examined and the direction of the ratio error is used for additional control. This provides very precise control of ratio and flow and helps prevent oscillation, hunting and other undesirable characteristics in such a system.

TECHNICAL FIELD

[0001] Devices for robotically dispensing sealants and adhesives on toparts have become increasingly popular in recent years.

BACKGROUND ART

[0002] Products such as Graco's PRECISIONFLO unit using technology suchas shown in U.S. Pat. No. 5,847,285, the contents of which areincorporated by reference, have become increasingly popular withautomotive manufacturers in order to provide precision application of abead of (single component) adhesive for various applications. Such unitstypically dispense at pressures ranging from around 600 PSI to 3000 PSI.Recently, the material manufacturers of such sealants and adhesives havebeen producing plural component materials which provide increasedperformance for the manufacturer.

[0003] It is therefore an object of this invention to provide adispensing apparatus which is capable of dispensing such pluralcomponent materials with the same precision as the single componentproducts and yet will maintain ratio assurance and integrity for mixingthe two materials.

DISCLOSURE OF THE INVENTION

[0004] Various parties involved in such manufacture use different termsfor the materials involved. The major component of the plural materialis also commonly referred to in the industry as the B component or theresin component. Similarly, the minor component is also often referredto as the A component, or activator, or catalyst.

[0005] Overall, the scheme can be characterized by saying first look atthe flow rate. If the flow rate is too high, decrease is needed on oneof the components so the ratio error is then looked at and the flowrate/pressure differential for the material which is there in excess isdecremented. Another level of control is provided in that the ratioerror is continually examined and the direction of the ratio error isused for additional control. This provides very precise control of ratioand flow and helps prevent oscillation, hunting and other undesirablecharacteristics in such a system.

[0006] These and other objects and advantages of the invention willappear more fully from the following description made in conjunctionwith the accompanying drawings wherein like reference characters referto the same or similar parts throughout the several views.

BRIEF DESCRIPTION OF DRAWINGS

[0007]FIG. 1A shows the general result of the flow calibration routinefor the major material.

[0008] FIG 1B shows the result of the flow rate calibration for theminor material.

[0009]FIG. 2 is a schematic representation of the dispensing apparatusof the instant invention.

[0010]FIG. 3 is a flow chart of the pressure control loop of the instantinvention.

[0011]FIG. 4 is a flow chart showing the volume compensation scheme.

BEST MODE FOR CARRYING OUT THE INVENTION

[0012] In use, the user sets the desired ratio, the maximum flow rate,and the number of volume updates per liter and the flow meter K factors(pulses/liter). Pressure loops are adjusted with Ki (integral) and Kp(proportional) gains independently for the major and minor materials.Pressure control of the two sides is performed on the basis of thepressure change between the outlet of the dispense valve and the inletof the mixer.

[0013] Gun calibration procedure is performed whereby major and minormaterials are calibrated at the same time independently. The calibrationroutine provides the delta pressure required to obtain the maximum flowof the major and minor materials. In the example here the materialrequires a ratio of 2:1 of major to minor materials. The maximum totalflow rate desired is 600 cc/minute. The calibration routine returns thedelta pressure required to achieve 400 cc/minute of major volume and thedelta pressure required to achieve 200 cc/minute of the minor volume.

[0014] Referring to the drawing figures, circled letters are shown whichrefer to portions marked in the attached source code. The pressurecontrol is relatively straight forward as set forth in FIG. 3. Theupdating of pressure and volume compensation occurs every 488microseconds. First, the volume for partial pulses is calculated byinterpolation when the actual volume integral is updated. Duringdispensing, each time a flow meter pulse is received, the actual volumeintegral is decremented by the cc/pulse of the respective meter.

[0015] As used herein the 1% referred to is 1% of the peak pressureresulting from the calibration routine. The robot then looks to see ifthe flow is in the upper or lower half of the total range. If in theupper half of the range (typically greater than a 6 volt robot command)the upper peak pressure point is adjusted and if less than or equal to 6volts, the zero offset value is adjusted. This discussion will onlyrefer to the robot command being greater than 6 volts or in the upperhalf of the pressure range however as can be seen from the FIG. 4 flowchart, the logic is similar for adjustment in the lower end.

[0016] As indicated, the actual volume integral is updated on a periodicbasis for both materials and a ratio error is then calculated. Initiallythe controller looks to see if the flow is too low. If the flow is toolow the controller looks to see if the error ratio is greater than zero,that is if there is too much major material and not enough minormaterial. If the error ratio is greater than zero, the peak pressure ofA is increased by 1%. The controller then looks to see if the errorratio is greater than the previous error ratio. If it is, the peakpressure of A is increased by an additional 1%. However if it is notgreater than the previous error ratio, that is, if it is coming backtoward the desired ratio, the peak pressure of B is increased by 1%. Ifthe ratio error is not greater than or equal to zero, that means thereis too much minor component and not enough major and the peak pressureof B is increased by 1%. The system then looks to see if the ratio erroris less than the previous ratio error and if it is the peak pressure ofB is increased by 1% and if not the peak pressure of A is increased by1%.

[0017] Similarly, it the flow is too high, the system looks at the errorratio and if less than zero the peak pressure of A is decreased by 1%.The system then looks to see if the ratio error is less than theprevious error and if it is the peak pressure of A is decremented by anadditional 1% and if not, the peak pressure of B is decremented by 1%.Similarly, if the ratio error is not less than zero, the peak pressureof B is decremented by 1% and if the ratio error is greater than orequal to the previous error the peak pressure of B is decremented by anadditional 1% and if not the peak pressure of A is decremented by 1%.

[0018] It is contemplated that various changes and modifications may bemade to the dispensing apparatus without departing from the spirit andscope of the invention as defined by the following claims.

1. A method for dispensing plural component materials comprised of major and minor components at relatively elevated pressures at a predetermined flow rate, a predetermined maximum flow and at a predetermined ratio, the method comprising the steps of: supplying said major and minor components at relatively elevated pressures; measuring the amount of flow of each of said major and minor components during a relatively short period of time; comparing the combined flow of said major and minor components during said period of time to said predetermined flow rate and if the measured flow rate is too high, examining the measured ratio and decrementing the flow for the material which is there in excess; and if the measured flow rate is too low, examining the measured ratio and incrementing the flow for the material which is insufficient.
 2. The method for dispensing plural component materials of claim 1 wherein said incrementing and decrementing are performed in amounts of a fixed percentage of said predetermined maximum flow.
 3. The method for dispensing plural component materials of claim 1 wherein the direction of change of ratio error formed by the difference between said predetermined ratio and said measured ratio is taken into account during correction. 